Plastic coated ferrule for a tube coupling

ABSTRACT

A plastic coated, positive-bite-type ferrule for a high-pressure tube coupling including cooperating body and closure members which engage the plastic coated ferrule therebetween to seal the coupling.

United States Patent Bucceri PLASTIC COATED FERRULE FOR A TUBE COUPLINGBernard J. Bucceri, Erie, Pa. Autoclave Engineers, Inc., Erie, Pa.

Sept. 10, 1969 Inventor:

Assignee:

Filed:

Appl. No.:

U.S. CL ..285/94, 285/34 1, 285/3827,

nu. Cl. ..Fl6l 197W Fleldolsearch ..277/235;2ss/ss, 341,342,

[151 3,643,984 5 Feb. 22, 1972 FOREIGN PATENTS OR APPLICATIONS 818,5876/1937 France ..285/382.7

Fabian et al. ..285/1 11 Primary Examiner-David .l. Williamowsky285/382], DIG. 10, Ill, 94

References Cited UNITED STATES PATENTS 6/1963 Wurzburger ..285/382.7 X

Assistant Examiner-David l-l. Corbin Attomey-Webb, Burden, Robinson &Webb [57] ABSTRACT 3 Claims, 1 Drawing Figure PATENTEDFEBZZ m2 3,643,984

l6 l9 iso Ms isa -12 J////ZV/ i l I INVE/VTO Bernard J. Bu H gr Mam/ UMHIS ATTORNEYS PLASTIC COATED FERRULE FOR A TUBE COUPLING This inventionrelates to a tube coupling and particularly to a coupling including asleeve or ferrule, and useful for a highpressure tube coupling.

Sleeveor ferrule-type tube couplings generally comprise a body having abore for receiving an end of a length of tubing. This body bore includesa flared portion which is suitably shaped to engage an end of a sleeveor ferrule which is slidably mounted on the tubing. A closure member isthreadably secured to the body and adapted to be tightened to compressthe ferrule and seat it securely in the body to seal the coupling.

A major factor tube in coupling seal failure has been the inability toclosely control the torque required to properly seat the ferrule in thetube coupling. Proper seating is a direct function of the amount oftorque, i.e., the tighter the seal desired, the greater the amount oftorque applied. Excessive torque results in adverse mechanical stressbeing put on the thread connection between the body and closure member,and wears and galls the threads to such an extent that the coupling,once made, cannot be opened and rescaled.

Additinally, excessive torquing of the coupling results in the lead orbiting end of the ferrule itself being galled or collapsed and destroyedbefore a proper seal is obtained. As a corrollary, however, reducing thetorque applied to the closure member may result in improper ferruleseating and lead to immediate or early failure of the coupling.

To limit the torque applied to an amount consistent with thread life ofthe connection and to eliminate galling of the coupling elements, I haveinvented a plastic coated sleeve or ferrule which is adapted to becompressed between cooperating body and closure coupling members in ahigh pressure tubing bite-type connection. I have discovered that theplastic coated ferrule not only improves thread life and avoids gallingsince less torque is required to seal the coupling permitting theconnection to be rescaled many times, but surprisingly facilitatesproper seating of the ferrule within the coupling and allows the leadingor biting edge of the ferrule to cut deeper into the tubing wallresulting in a more efficient sealed coupling.

The art has employed dissimilar materials for the sleeve, body andtubing in an effort to avoid electrolytic action between the couplingelements. This has often reduced the life of the ferrule, particularlyin corrosive environments where certain of the ferrule materials havebeen severely chemically attacked. The same materials can be used forall elements of my coupling.

The plastic coating used on my ferrule should be characterized by highlubricity and be substantially inert relative to the elements of theconnection as well as to fluids with which it may come in contact inapplication. I have used and prefer a tetrafluoroethylene polymermanufactured by E. I. du Pont de Ncmours and Company under the trademarkTeflon-S. Properly applied and cured in accordance with the method ofcoating hereinafter disclosed, this material exhibits satisfactorycharacteristics for use in sleeve or ferrule-type tube couplings.

In the accompanying drawing, I have shown in longitudinal cross sectionone-half of a typical sleeveor ferrule-type coupling including a plasticcoated ferrule l in accordance with my invention. The coupling comprisesa body 2 having an axial passageway 3 for channeling fluid through thebody from or into a length of tubing 4 which is positioned in areceiving bore 5 of the body and in communication with passageway 3. Themouth of the receiving bore 5 is flared outwardly forming afrustoconical surface 6. An axial bore 7 extends from the mouth to theouter wall of the body. A major portion of the bore 7 carries internalthreads 8. A closure member or gland nut 9, having external threads 10,is positioned on tubing 4 and threadably engaged to the threads 8 of thebore. The gland nut includes a central bore ll having a diameterslightly greater than the outer diameter of the tubing 4 so that thetubing 4 can pass through bore 11. A flared surface 12 is also formed onthe inner wall 13 of the gland nut. A chamfer I4 is provided on the endof the gland nut to facilitate threading the nut into the body bore 7.

A hollow sleeve or ferrule 1, according to may invention, is mounted onthe tubing 4 and is adapted for compression, upon tightening of thegland nut into the body, between the surface 6 of the body and theflared surface 12 of the gland nut. Bore 15 of the ferrule closely fitsaround the tubing 4. The leading end of the ferrule 1 includes anannular recess 16 forming a thin annular extension 17 which carries anexternal sealing surface 18. The intersection of the bore 15 and therecess 16 defines a sharp annular edge 19. The leading end of theferrule shown in solid lines illustrates its position when the ferruleis not under compression. The dotted lines show the position of theleading end when the ferrule is advanced under compression by torquingthe gland nut into the body, for example, when the gland nut isfingertight. The trailing end of the ferrule 1 also includes afrustoconical sealing surface 20 for engaging the gland nut surface 12upon tightening of the gland nut into the body. As the nut is threadedinto the body, the fe rrule 1 is compressed tightly between the flaredsurfaces 6, l2, and the sharp edge 19 of the ferrule bites into thetubing to effect a positive seal through the tube coupling.

I have found through extensive comparative testing that excessive torqueis required, attended by the problems previously set forth, to obtainthis positive biting engagement when a dry or uncoated sleeve or ferruleis used. Further, I have discovered that these problems can besubstantially eliminated by applying to the ferrules a plastic coating15a, preferably Teflon-S," according to the following method:

The ferrule, preferably of stainless steel material, is first surfacetreated by sandblasting and subsequently is fire cleaned.Tetrafluorethylene polymer material, specifically Teflon-S," is thenapplied to the exterior surfaces of the ferrule using a controlled spraytechnique well known in the art. The coating 15a extends around thebiting edges of the ferrule at each end and extends a short distanceinto the bore. The center portion of the inside wall or bore 15 of theferrule l is not coated. A coating of approximately 2 mil thickness hasbeen found satisfactory.

vThose skilled in the art will appreciate that the curing schedule for aplastic coating depends upon the quality of the coating and bondingrequired to withstand the environmental conditions to which the coatedferrule will be exposed. l have found that ferrules baked for 15 minutesat approximately 400 F. and then for 20 minutes at 650 F. to insureproper bonding and curing of the plastic coating are particularlysuitable for use under conditions of moderate abrasion whcrc operatingtemperatures do not exceed 500 F.

Tests have shown that less torque is required to effect a positive sealwith my plastic coated ferrule than with an uncoated ferrule in the sametube coupling. Moreover, with plastic coated ferrules, according to myinvention, less stress is placed on the bearing areas of the couplingelements, and galling is substantially eliminated. A considerable savingin assembly time is realized by using plastic coated ferrules instead ofuncoated ferrules, since the use of mandrels and lubrication compounds,previously needed for assembly of the coupling, are not required. Beloware the pertinent procedures used and the results obtained from thesetests:

a. Four drop forged valve fitting incorporating uncoated 316 CW ferrulesof each of one-fourth, three-eighths and one-half inch sizes wereassembled on 304 SS annealed tubing with gland nuts initially positionedat fingertightness. Torque was applied to tighten each of the nuts to aposition 1% turns past fingertightness. The torque required to tightenwas recorded at one-fourth turn intervals during assembly. Each assemblywas then checked for leakage, using nitrogen, at its own workingpressure; each assembly was also proof checked and burst with water.Proof and bursting pressures were recorded.

b. Four drop forged valve fittings have uncoated l7-4Ph ferrules of eachof one-fourth, three-eighths and one-half inch sizes were assembled on304 SS annealed tubing with the gland nuts initially flngertight. Thenuts were then torqued to a position l A turns past finger tightness.Torquing and proof testing were .carried out as in (a) above andrecorded.

c. Four drop forged valve fitting incorporating 316 CW plastic coatedferrules. in accordance with my invention. of each of one-fourth.three-cighths. and one-half inch sizes were assembled on 304 SS annealedtubing, torque tested, leak and burst tested following the proceduresset forth in (a) above. The torque to tighten was recorded at one-fourthturn intervals.- Proof and bursting pressures were also recorded.

d. Four drop forged valve fittings having 17-4Ph ferrules. plasticcoated in accordance with my invention, of each of one-fourth,three-eighths and one-half inch sizes were assembled on 304 SS annealedtubing following the procedure set forth in (a) above. Torque, proof andburst pressure data was recorded.

Tables I-Vl below give the data obtained from the torquing tests. Theobservations made during the tests and the results shown for uncoatedand my plastic coated ferrules based upon the data obtained are setforth below in each Table.

Tests were also performed to evaluate the expansion of the male threadon the drop forged fitting when using uncoated ferrules and ferrulesplastic coated in accordance with my invention. Four fittings of eachsize one-fourth. three-eighths and one-half inch with uncoated ferrulesand ferrules having my plastic coating were assembled on 304 SS annealedtubing. Dimensioned measurements of the threaded connection were madeand recorded before assembly and at every one-fourth turn past fingertightness. The data recorded also appears on Tables l-Vl. in general,the results of this test show that the threads of the tube coupling werestressed more using uncoated ferrules over plastic coated ferrules.

TABLE! 316CWferrules-%"x%r". 304 SS tubing 80B Brinnell. Proof (N 6.000p.s.i./Prof(H O) 12,000 p.s.i.

Burst Thread Thread (H 0) dia. dia.

Torque 24.000 before after Turn valve in pounds min. make-up make-upUncoated:

Vs-1%. 50-480 56.000 .556 .557 '/4-1% 50-480 54.000 .556 .557 At-1 A50-475 54.000 .556 .557 /4--l A 50-480 54.000 .556 .557 Average 0-479With plastic coating:

/4-1%.... 6 -480 56.000 .557 .559 /a-lki. 60-420 56.000 .557 .55913-184. 50-410 56,000 .557 .5575 14-114. 60-440 59.000 .556 .558Average. 58-437 The torque for four assemblies ranged between 50 and 479in. lbs. There was no leakage during proofs. The average tube burst at55.000 psi.

TABLE ll 316 CW Ferrules-W' x W. 304 SS Tubing 84B Brinnell. Proof (N6.000 psi/Proof (H2O) 12.000 p.s.i.

The torque for four assemblies ranged between 58 and 437 in. lbs. Therewas no leakage during proofs. The average tube burst at 55.000 psi.

LII

316 (:W Ferrules V1" 1 W. 304 SS Tubing 74B Hrinnell. Proof (N 6.000p.s.i./Proof(H-,()) 12.000 [1.5.1.

Burst Thread Thread (H O) dia. dia. Torque 24.000 before after 'lui'nvalve in pounds min. make-up make-up U neoated:

'/4 l A; 1 35- 1440 28 .000 .807 .809 fit-1V4 -1440 27.000 .810 .812At-1%.. I3)- 1430 27.000 .808 .811 'A- l 4.. -1450 27.000 .808 .812Average 137-1440 With plustn coating:

At-1%.. 80-840 28.000 .807 .8085 /4--l '/-i.. 80-840 28.000 .808 .810Kt-1%.. 80-840 28.000 .806 .80! Kt-l '10.. 80-820 27.000 .808 .810Average. 80-835 The results for '6" sleeves followed the exact patternas the W sleeve. above except for torque.

TABLE IV 17-4 lh Ferrules-W' x W. 304 SS Tubing 80B Brinnell. Proof (N 16000 [1.s.i./l'roof(H- 12.000 p.s.i.

Burst lhread 'l'hrcud (H- diu. diu. 'lorquc 24.000 before alter 'l'urnvalve in pounds min. make-up make-up Uncoated:

/4-1'Aa 88-360 56.000 .556 .557 '/4 l A... l04-540 56.000 .556 .561 'A-lA 89-480 56.000 .556 .559 A-I'A... 103-520 56.000 .556 .560 Average96-475 With plastic coating:

4- 1 A 73-420 55.000 .557 .558 Kt-1%... 73-420 55.000 .557 .5585 4-1 A73-430 55 .000 .557 .559 /4l 73-420 56.000 .557 .559 Average... 73-423The torque for four assemblies ranged between 73 and 423 in. lbs. for myplastic coated sleeve. and )6 to 475 in. lbs. for the uncoated sleeves.There was no leakage with'the plastic coated sleeves. although twoconnections having uncoated ferrules leaked because of galling ofmaterials at the seating area.

TABLE V 17-4 Ph Fcrrules-W x 'A". 304 SS Tubing 84B Brinnell. Proof (N116.000

p.s.1./Proof(H-,()) 12,000 psi. m

The torque for the four each assemblies ranged between 84 and 739 in.lbs. for the 316 CW uncosted sleeves. The torque for the four each ofthcassemblies ranged between 107 and 715 in. lbs. for the coated sleeves.and 151 to 1.360 for the uncoaled sleeves. There was no leakage with thecoated sleeves. but one assembly 1) did lctik gas at its own workingpressure of 6.000 psi.

TABLEVl The results for A sleeves followed the exact pattern as thesleeve, except for torque. H

The temperature characteristics of a plastic coated ferrule, accordingto my invention, were also determined by testing 6. fittings. Reducedtorque requirements enable the assembler to advance the sealing glandnut the proper distance along a tubing into a body without excessiveforce and possible damage to the gland or body threads. This reducedtorques-g at'oids galling of the threads and ferrule enabling theassembly to be opened and resealed a number of times. Finally, a moreefficient coupling is obtained using my plastic coated ferrule over acoupling having an uncoated ferrule. Reduced friction in my ferruleassembly permits the leading edge of the ferrule to bite or cut deeperinto the tubing wall than do ferrules now in use providing a positiveseal in my coupling.

Particularly, 1 have discovered that a ferrule properly plastic coatedwith Teflon according to my method achieves all of the foregoingadvantages and the specific method of providing a Teflon ceramic coatingas disclosed herein should be considered a preferred form of theinvention.

1 claim:

1. In a fitting for a high-pressure tubing including a body memberhaving an opening for receiving an end of a length of tubing, a closuremember surrounding the tubing and adapted to be threadably secured tothe body member, each of said body and closure members being providedwith opposed substantially frustoconical flared surfaces, theimprovement comprising a metallic ferrule means, having a boretherethrough each of the fitting sizes one-fourth three-eighths andone-half and Sealing Surfaces, one at each end for mating with said inchat 500 F. and 800 F. Torques were applied when cold and recorded. TableV11 shows the data obtained. In every case, after the test, the fittingwas disassembled and the coating was observed to be satisfactory.

From the foregoing data, it is apparent that several advantages areobtained from use of my plastic coated ferrule over uncoated ferrulesknown to the art. Specifically, less torque is required to properlyassemble a fitting incorporating my plastic coated ferrule than onehaving an uncoated ferrule. Based upon the data herein, in some casesthe torque required isredusqq ..HB9E 5. .9..E. GEFYEJQBH QFEQEPlg flaredsurfaces of the body and closure member and surrounding the tubingbetween the opposed flared surfaces, adapted to be compressed betweenthe members upon threadably tightening the closure into the body member,whereby tightening of the closure into the body member advances theferrule along the tubing to force the sealing surfaces into face-to-faceengagement with the flared surfaces, said engagement causing a portionof a sealing surface to bite into the tubing to effect a fluid sealthrough the fitting, a plastic coating being bonded to the ferrule meanson its exterior surface and extending at least a short distance intoeach end of the bore, said plastic coating being characterized by highlubricity and substantial inertness to its environment.

2. The improvement as set forth in claim 1 in which an end of theferrule means includes a circumferential extension which carries one ofthe sealing surfaces and defines a recess which terminates in a sharpannular edge adjacent the tubing, said engagement causing the sharp edgeto bite into the tubing.

3. The improvement in a ferrule means as set forth in claim '1 in whichplastic coating is tetrafluoroethylene copolymer material.

1. In a fitting for a high-pressure tubing including a body memberhaving an opening for receiving an end of a length of tubing, a closuremember surrounding the tubing and adapted to be threadably secured tothe body member, each of said body and closure members being providedwith opposed substantially frustoconical flared surfaces, theimprovement comprising a metallic ferrule means, having a boretherethrough and sealing surfaces, one at each end for mating with saidflared surfaces of the body and closure member and surrounding thetubing between the opposed flared surfaces, adapted to be compressedbetween the members upon threadably tightening the closure into the bodymember, whereby tightening of the closure into the body member advancesthe ferrule along the tubing to force the sealing surfaces intoface-to-face engagement with the flared surfaces, said engagementcausing a portion of a sealing surface to bite into the tubing to effecta fluid seal through the fitting, a plastic coating being bonded to theferrule means on its exterior surface and extending at least a shortdistance into each end of the bore, said plastic coating beingcharacterized by high lubricity and substantial inertness to itsenvironment.
 2. The improvement as set forth in claim 1 in which an endof the ferrule means includes a circumferential extension which carriesone of the sealing surfaces and defines a recess which terminates in asharp annular edge adjacent the tubing, said engagement causing thesharp edge to bite into the tubing.
 3. The improvement in a ferrulemeans as set forth in claim 1 in which plastic coating istetrafluoroethylene copolymer material.